theo j.m. zouros university of crete & iesl-forth heraklion, crete

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Zero -degree Auger Projectile Spectrometry in the New Experimental Storage Ring: Challenges and Prospects. Theo J.M. Zouros University of Crete & IESL-FORTH Heraklion, Crete. Motivation: High resolution electron spectrometry in the NESR. - PowerPoint PPT Presentation

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  • Zero-degree Auger Projectile Spectrometry in the New Experimental Storage Ring:Challenges and Prospects Theo J.M. ZourosUniversity of Crete & IESL-FORTH Heraklion, Crete

    SPARC-Paris, February 12-15, 2007

  • Motivation: High resolution electron spectrometry in the NESR Auger and conversion lines of high-Z few-electron ions produced in collisions with atoms - No measurements for ions!!! (only neutral targets to date) - Charge state q-dependence high precision Binding Energy determination of atomic levels Physics of strong fields: - Collision dynamics, state-selective cross section determination - Atomic Structure of high-Z few-electron ions (relativistic effects)This will require electron observation in the beam direction known as Zero-degree Auger Projectile Spectroscopy (ZAPS)Of relativistic electrons with lab energies up to about 0.5 MeVCombined with a spectrometer resolution of p/p 10-4 access to the natural line widths should also be possible

    SPARC-Paris, February 12-15, 2007

  • The NESR: the ultimate fantasy for atomic collisions physics? NESR Circumference: 221.11 m Vacuum: 10-11 mbar Ion energies: 4 -740 MeV/u Ion beam species: H U Radioactive beams: yes Ion charge states: /q 2.7 Number of ions: ~108 Beam particle current: ~1013 #/s Emittance: 0.1 1 mm-mrad Momentum p/p (cooled): 10-4 Gas-jet target (extrapolation from ESR) Areal Density: 1012-1013 #/cm2 Length: 1.4 - 4 mm Background pressure: 10-9 mbar~ 9 m

    SPARC-Paris, February 12-15, 2007

  • Two different electron spectroscopiesZero-degree Auger Projectile e- Spectroscopy (ZAPS) used successfully since the 1980s primarily at Tandems to measure Auger electrons from projectiles excited via capture, excitation or ionization and combinations emitter: low-Z HCI ions in the 0.1- 3 MeV/u collision regime electrostatic spectrometers: lab electron energies = 0-6 keV and R= / ~0.1% -ray spectroscopy used successfully in the 1950-1970s at high flux reactors or with radioactive sources to measure conversion and Auger electrons emitter: stationary high-Z neutral activated target atoms large radius (e.g. 50cm Uppsala, 100cm Chalk River, 50cm BILL) double focusing magnetic spectrometers: lab electron energies 3 MeV and Rp= p/p ~ 0.01- 0.05% The SPARC electron spectroscopy initiative is expected to combine both expertise

    SPARC-Paris, February 12-15, 2007

  • Traditional 00 e- spectrometer two-stage 450 parallel plate with intermediate deceleration stageIon BeamGas CellFaraday CupDeflectorelectronsDecel stagePressure GaugeGas inSignalAnalyzerDetector Robust operation Voltages scanned to acquire spectrum High resolution ~0.1% uses deceleration stage with fixed pass energy/=3%

    SPARC-Paris, February 12-15, 2007

  • Advantages of 00 Auger projectile spectrometry (ZAPS) Only a single pre-selected Projectile charge state involved - considerable simplification of lines in spectrum no line blending (mixture of different charge states) - ion surgery collisions with low-Z few-electron targets (He, H2) - very successful in isoelectronic studiesQuestion: How can ZAPS be done effectively in the NESR? High resolution technique with relatively high overall efficiency - /~0.1%, ~10, ~10-4 sr - Resolution good enough to resolve most K-Auger lines - Much more efficient than comparable resolution crystal X-ray spectrometers (for low-Z ions high Auger yield, no window absorption, large ) Determination of absolute double differential cross sections - collisional energy dependence of well defined transition Deceleration stage provides useful variable resolution - low resolution or high resolution can be used as needed

    SPARC-Paris, February 12-15, 2007

  • Important features of 00 Electron emission spectrumLow energy Target e- continuumCusp e- at v = Vp High energy Projectile e- continuumBroad Binary Encounter e- PeakKinematically shifted Auger Projectile e- linesBackwardemissionForwardemission

    SPARC-Paris, February 12-15, 2007

  • Kinematics: Instrumental Line Broadening IFor >00 ~ , while for =00 ~ 2 thus substantial gains in resolution can be attained by going to =00 observation angle

    SPARC-Paris, February 12-15, 2007

  • Kinematics: Instrumental Line Broadening IIAt 00 the kinematic broadening grows with projectile velocity Vp grows approximately as 2 diminishes with Auger energy

    SPARC-Paris, February 12-15, 2007

  • Comparison of Tandem - NESRTypical Beam and Target operational parametersNESR advantages (+) vs disadvantages (-)(+) High particle current, increases with collision energy(-) jet target: smaller density and effective length (but note Grisenti talk on liquid targets) Question: Possibility of cell target? Would increase rate by at least x500!*projected from experience with ESR jet target** Assuming a constant 108 particles in the NESR over the 4-740 MeV/u energy range and for q=92

    SPARC-Paris, February 12-15, 2007

  • Ion BeamGas inPressure GaugeGas CellPSD-RAEX-PositionY- PositionTiming4-element lensFaraday Cupelectrons PSD: x 100 -700 higher sensitivity E acceptance ~ 20% 4-element lens for deceleration and focusing Resolution ~ 0.05-0.1% = 1.8 x 10-4 sr ( = 0.8680)Technical developments: 2-D PSD with 4-element lens +doubly differentially pumped gas cellThe Univ. of Crete ZAPS spectrometerAt Kansas State U.Turbo pump

    SPARC-Paris, February 12-15, 2007

  • Dedicated machines requiring huge housingTo ensure field uniformity and easy access ray spectroscopy Bzr

    SPARC-Paris, February 12-15, 2007

  • 50cm 1/r BILL electron iron-core spectrometerNatural widthp/p=1x10-5Slit widths:Entry = s1Exit = s2s1=s2 = 0.2 mm

    =50 cm

    Best resolution p/p = 7.6 x 10-5

    SPARC-Paris, February 12-15, 2007

  • Use in storage rings: The ultimate ZAPS? Ultimate resolution: p/p < 10-4 Lab e- energy: 3-500 keVEnvisioned two-stage magnetic spectrometer(original ESR proposal Rido Mann et al 1988 GSI)1st stage (deflector) low dispersion, low resolution uniform field dipole target spot size 1mm x 1mm large angular acceptance 5-1002nd stage high dispersion, high resolution r-n Bz-field (n=1 BILL, n=2 Chalk River) entry slit widths ~0.1-1 mm small angular acceptance 0.1-0.50 2-D PSD

    SPARC-Paris, February 12-15, 2007

  • Resolution contributions=100eV, =80keV, =0.20 (full-acceptance)Projectile p/p = 5 x 10-5, Spectrometer p/p = 1 x 10-4

    SPARC-Paris, February 12-15, 2007

  • ConclusionsImportant technical issues to take into consideration/resolve: Iron or Air -core magnet design? - Air-core seems better but needs more space! - Iron -core: problem of magnetic field uniformity over 1 m radius? problem of Remanent magnetization? Solid angle considerations - small ~0.10 (to limit kinematic broadening for line width measurements) will severely limit count rate PSD necessary Good design, optical alignment and slit/baffle controls will be critical High quality non-magnetic materials to be used in the entire target area Need for highest areal density target (liquid H2/He)? At the 10-5 precision level - Earth magnetic field annulment (-metal shielding/large Helmholtz coils?) - Temperature stability to ~0.10 CAnybody up to the challenge? Come join the SPARC electron spectroscopy group!http://www.gsi.de/fair/experiments/sparc/electron-spectrometers_e.html

    SPARC-Paris, February 12-15, 2007

  • BibliographyN. Stolterfoht, Phys. Rep. 146 (1987) 315-424.T.J.M. Zouros and D.H. Lee, in Accelerator -Based Atomic Physics Techniques and Applications, ed. S. Shafroth and J.C. Austin, AIP, Chapter 13 (1997) p. 427-479.E.P. Benis et al. Phys. Rev. A 69 (2004) 052718.W. Mampe et al., NIM 154 (1978) 127-149.R.L. Graham, G.T. Ewan and J.S. Geiger, NIM 9 (1960) 245-286.For more information also check my home page:http://www.physics.uoc.gr/~tzouros

    SPARC-Paris, February 12-15, 2007

  • XX International Symposium on Ion-Atom collisions* andSPARC topical meeting on Electron spectrometry in the NESRAugust 1-4, 2007Agios Nikolaos, Crete, GREECE*a satellite of XXV ICPEAC - Freiburg

    SPARC-Paris, February 12-15, 2007

  • Resolution contributions=10eV, =50keV, =0.20 (full-acceptance)Projectile p/p = 5 x 10-5 , Spectrometer p/p = 1 x 10-4

    SPARC-Paris, February 12-15, 2007

  • Resolution contributions=10eV, =1keV, =0.20 (full-acceptance)Projectile p/p = 5 x 10-5 , Spectrometer p/p = 1 x 10-4

    SPARC-Paris, February 12-15, 2007

  • Kinematics: energy shifting and doubling IIFor He-like UraniumK-Auger series energies(75 -130 keV rest) frameRange in Lab from about - 1000 keV (+)40 - 0 keV (-)For projectile energies4 -740 MeV/u

    SPARC-Paris, February 12-15, 2007

  • Angular compression beamingAt 740 MeV/u we have:For =1000 eV, max = 2.4070 = 10 eV, max = 0.240

    Strong beaming for small electron energiesPractically total cross section measured around 00All differential information averaged out

    SPARC-Paris, February 12-15, 2007

  • Kinematics: Line stretching and enhancingNatural Line widths (rest frame) areChanged to widths in Lab frame Mild enhancement and stretching in momentum analysis!!PE=7 eVRanal=3%

    SPARC-Paris, February 12-15, 2007

  • Kinematic Widths and Enhancement factorsFor atomsK line-widths dominated by Radiative widths at high ZAnd Auger widths at low ZWhat about Highly Charged Ions?Momentum widths are stretched only weaklyWhile energy widths a lot!

    SPARC-Paris, February 12-15, 2007

  • Zero-degree Auger Pr

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